Cancer arises when a normal cell undergoes neoplastic transformation and becomes a malignant cell. Transformed (malignant) cells escape normal physiologic controls specifying cell phenotype and restraining cell proliferation. Transformed cells in an individual's body thus proliferate in the absence of these normal controls, thus forming a tumor.
When a tumor is found, the clinical objective is to destroy malignant cells selectively while mitigating any harm caused to normal cells in the individual undergoing treatment. Chemotherapy is based on the use of drugs that are selectively toxic (cytotoxic) to cancer cells. Several general classes of chemotherapeutic drugs have been developed, including drugs that interfere with nucleic acid synthesis, protein synthesis, and other vital metabolic processes.
Susceptibility of an individual neoplasm to a desired chemotherapeutic drug or combination of drugs often, however, can be accurately assessed only after a trial period of treatment. The time invested in an unsuccessful trial period poses a significant risk in the clinical management of aggressive malignancies. Therefore, it is of importance to assess the expression status of genetic determinants targeted by specific chemotherapeutic agents. For example, if a tumor expresses high levels of DNA repair genes, it is likely that the tumor will not respond well to low doses of DNA-damaging genotoxic agents. Thus, the expression status of genetic determinants of a tumor will help the clinician develop an appropriate chemotherapeutic regimen specific to the genetic repertoire of the tumor.
As the single most effective agent for the treatment of colon, head and neck, and breast cancers, the primary action of 5-fluorouracil (5-FU) is to inhibit thymidylate synthase activity (Moertel, C. G. New Engl. J. Med., 330:1136-1142, 1994). For more than 40 years the standard first-line treatment for colorectal cancer was the use of 5-FU alone, but it was supplanted as “standard of care” by the combination of 5-FU and CPT-11 (Saltz et al., Irinotecan Study Group. New England Journal of Medicine. 343:905-14, 2000). Recently, the combination of 5-FU and oxaliplatin has produced high response rates in colorectal cancers (Raymond et al., Semin. Oncol., 25:4-12, 1998). We have previously shown that advanced stage colorectal tumors expressing high levels of thymidylate synthase (TS) responded poorly when treated with 5-FU/leucovorin. Thus, the patients' survival was low compared to those without elevated TS expression. (Leichman et al., J. Clin Oncol., 15: 3223-3229, 1997).
The mechanism of action and the metabolic pathway of 5-FU have been intensively studied over the years to identify the most important biochemical determinants of the drug's anti-tumor activity. The ultimate goal was to improve the clinical efficacy of 5-FU by a) modulation of its intracellular metabolism and biochemistry and b) measuring response determinants in patients' tumors prior to therapy to predict which patients are most likely to respond (or not to respond) to the drug. Two major determinants emerged from these studies: 1) the identity of the target enzyme of 5-FU, thymidylate synthase (TS) and 2) the identity of the 5-FU catabolic enzyme, dihydropyrimidine dehydrogenase (DPD).
The first studies in the area of tumor response prediction to 5-FU based therapy centered on the target enzyme TS in colorectal cancer. Leichman et al (Leichman et al., J. Clin Oncol., 15:3223-3229, 1997) carried out a prospective clinical trial to correlate tumor response to 5-FU with TS gene expression as determined by RT-PCR in pre-treatment biopsies from colorectal cancers. This study showed: 1) a large 50-fold range of TS gene expression levels among these tumors, and 2) strikingly different levels of TS gene expression between responding and non-responding tumors. The range of TS levels of the responding groups (0.5-4.1×10−3, relative to an internal control) was narrower than that of the non-responding groups (1.6-23.0×10−3, relative to an internal control). The investigators determined a resulting “non-response cutoff” threshold level of TS expression above which there were only non-responders. Thus, patients with TS expression above this “non-response cutoff” threshold could be positively identified as non-responders prior to therapy. The “no response” classification included all therapeutic responses with <50% tumor shrinkage, progressing growth resulting in a >25% tumor increase and non-progressing tumors with either <50% shrinkage, no change or <25% increase. These tumors had the highest TS levels. Thus, high TS expression identifies particularly resistant tumors. TS expression levels above a certain threshold identified a subset of tumors not responding to 5-FU, whereas TS expression levels below this number predicted an appreciably higher response rate, yet did not specifically identify responding tumors.
Subsequent studies investigated the usefulness of DPD expression levels as a tumor response determinant to 5-FU treatment in conjunction with TS expression levels. DPD is a catabolic enzyme which reduces the 5,6 double bond of 5-FU, rendering it inactive as a cytotoxic agent. Previous studies have shown that DPD levels in normal tissues could influence the bio-availability of 5-FU, thereby modulating its pharmacokinetics and anti-tumor activity (Harris et al., Cancer Res., 50: 197-201, 1990). Additionally, evidence has been presented that DPD levels in tumors are associated with sensitivity to 5-FU (Etienne et al., J. Clin. Oncol., 13: 1663-1670, 1995; Beck et al., Eur. J. Cancer, 30: 1517-1522, 1994). Salonga et al, (Clin Cancer Res., 6:1322-1327, 2000, hereby incorporated by reference in its entirety) investigated gene expression of DPD as a tumor response determinant for 5-FU/leucovorin treatment in a set of tumors in which TS expression had already been determined. As with TS, the range of DPD expression among the responding tumors was relatively narrow (0.6-2.5×10−3, 4.2-fold; relative to an internal control) compared with that of the non-responding tumors (0.2-16×10−3, 80-fold; relative to an internal control). There were no responding tumors with a DPD expression greater than a threshold level of about 2.5×10−3. Furthermore, DPD and TS expression levels showed no correlation with one another, indicating that they are independently regulated genes. Among the group of tumors having both TS and DPD expression levels below their respective “non-response cut-off” threshold levels, 92% responded to 5-FU/leucovorin. Thus, responding tumors could be identified on the basis of low expression levels of DPD and TS.
DPD is also an important marker for 5-FU toxicity. It was observed that patients with very low DPD levels (such as in DPD Deficiency Syndrome; i.e. thymine uraciluria) undergoing 5-FU based therapy suffered from life-threatening toxicity (Lyss et al., Cancer Invest., 11: 2390240, 1993). Indeed, the importance of DPD levels in 5-FU therapy was dramatically illustrated by the occurrence of 19 deaths in Japan from an unfavorable drug interaction between 5-FU and an anti-viral compound, Sorivudine (Diasio et al., Br. J. Clin. Pharmacol. 46, 1-4, 1998). It was subsequently discovered that a metabolite of Sorivudine is a potent inhibitor of DPD. This treatment resulted in DPD Deficiency Syndrome-like depressed levels of DPD which increased the toxicity of 5-FU to the patients (Diasio et al., Br. J. Clin. Pharmacol. 46, 1-4, 1998).
Thus, because of a) the widespread use of 5-FU protocols in cancer treatment, b) the important role of DPD expression in predicting tumor response to 5-FU and c) the sensitivity of individuals with DPD-Deficiency Syndrome to common 5-FU based treatments, it is clear that accurate determination of DPD expression levels prior to chemotherapy will provide an important benefit to cancer patients.
Another class of chemotherapeutic agents specifically inhibits tumor cell proliferation by attenuating mitogenic signaling through receptor tyrosine kinases (RTKs), in cells where RTKs are over active. (Drugs of the Future, 1992, 17, 119). Receptor tyrosine kinases (RTKs) are important in the transduction of mitogenic signals. RTKs are large membrane spanning proteins which possess an extracellular ligand binding domain for growth factors such as epidermal growth factor (EGF) and an intracellular portion which functions as a kinase to phosphorylate tyrosine amino acid residues on cytosol proteins, thereby mediating cell proliferation. Various classes of receptor tyrosine kinases are known based on families of growth factors which bind to different receptor tyrosine kinases. (Wilks, Advances in Cancer Research, 1993, 60, 43-73)
Class I kinases such as the EGFR family of receptor tyrosine kinases include the EGF, HER2-neu, erbB, Xmrk, DER and let23 receptors. These receptors are frequently present in common human cancers such as breast cancer (Sainsbury et al., Brit. J. Cancer, 1988, 58, 458; Guerin et al., Oncogene Res., 1988, 3, 21), squamous cell cancer of the lung (Hendler et al., Cancer Cells, 1989, 7, 347), bladder cancer (Neal et al., Lancet, 1985, 366), oesophageal cancer (Mukaida et al, Cancer, 1991, 68, 142), gastrointestinal cancer such as colon, rectal or stomach cancer (Bolen et al., Oncogene Res., 1987, 1, 149), leukaemia (Konaka et al., Cell, 1984, 37, 1035) and ovarian, bronchial or pancreatic cancer (European Patent Specification No. 0400586). As further human tumor tissues are tested for the EGF family of receptor tyrosine kinases it is expected that its widespread prevalence will be established in other cancers such as thyroid and uterine cancer.
Specifically, EGFR tyrosine kinase activity is rarely detected in normal cells whereas it is more frequently detectable in malignant cells (Hunter, Cell, 1987, 50, 823). It has been more recently shown that EGFR is overexpressed in many human cancers such as brain, lung squamous cell, bladder, gastric, breast, head and neck, oesophageal, gynaecological and thyroid tumours. (W J Gullick, Brit. Med. Bull., 1991, 47, 87). Receptor tyrosine kinases are also important in other cell-proliferation diseases such as psoriasis. EGFR disorders are those characterized by EGFR expression by cells normally not expressing EGFR, or increased EGFR activation leading to unwanted cell proliferation, and/or the existence of inappropriate EGFR levels. The EGFR is known to be activated by its ligand EGF as well as transforming growth factor-alpha (TGF-a).
Inhibitors of receptor tyrosine kinases EGFR are employed as selective inhibitors of the growth of mammalian cancer cells (Yaish et al. Science, 1988, 242, 933). For example, erbstatin, an EGF receptor tyrosine kinase inhibitor, reduced the growth of EGFR expressing human mammary carcinoma cells injected into athymic nude mice, yet had no effect on the growth of tumors not expressing EGFR. (Toi et al., Eur. J. Cancer Clin. Oncol., 1990, 26, 722). Various derivatives of styrene are also stated to possess tyrosine kinase inhibitory properties (European Patent Application Nos. 0211363, 0304493 and 0322738) and to be of use as anti-tumor agents. Two such styrene derivatives are Class I RTK inhibitors whose effectiveness has been demonstrated by attenuating the growth of human squamous cell carcinoma injected into nude mice (Yoneda et al., Cancer Research, 1991, 51, 4430). It is also known from European Patent Applications Nos. 0520722 and 0566226 that certain 4-anilinoquinazoline derivatives are useful as inhibitors of receptor tyrosine kinases. The very tight structure-activity relationships shown by these compounds suggests a clearly-defined binding mode, where the quinazoline ring binds in the adenine pocket and the anilino ring binds in an adjacent, unique lipophilic pocket. Three 4-anilinoquinazoline analogues (two reversible and one irreversible inhibitor) have been evaluated clinically as anticancer drugs. Denny, Farmaco 2001 January-February; 56(1-2):51-6. Recently, the U.S. FDA approved the use of the monoclonal antibody trastazumab (Herceptin®) for the treatment of HER2-neu overexpressing metastatic breast cancers. Scheurle, et al., Anticancer Res 20:2091-2096, 2000.
Chemotherapy against tumors often requires a combination of agents such as those described above. Accordingly, the identification and quantification of determinants of resistance or sensitivity to each single drug has become an important tool to design individual combination chemotherapy.
Moreover, the search for genetic differences between primary tumors and metastases has been intensely pursued. Differential gene expression between a tumor and its metastases not only underlies the mechanism of tumor metastasis, but more importantly to the clinician, it determines the efficacy of chemotherapeutic agents on the primary tumor and matched metastases. Whereas primary tumor specimens are generally available either as pre-treatment paraffin-embedded biopsies or as resection specimens, in many cases, and especially in earlier stages of cancer, metastases are not readily detectable and biopsy specimens of matched tumor metastases on which phenotypic analyses could be performed would thus not be available. Therefore, it is important to determine the degree of variation of gene expression between primary tumors and metastases. This information is vital in order to determine whether or not a particular chemotherapeutic would be an effective therapeutic against the both the primary tumor as well as the metastases.
To date there has been no reliable way of determining whether a particular chemotherapy directed toward the expression of a tumor gene determinant appropriate for a primary tumor is also appropriate for treating a metastsis. Currently, the only way to reach such a conclusion was to have a fresh or frozen tissue biopsy of both the primary tumor and its metastasis. This would require a biopsy of primary tumor and matching tumor metastases. Unfortunately, because tumor metastases are often difficult to reach by standard surgical procedures and often only at great risk to the patient, it was previously not possible to determine whether a treatment regiment for the primary tumor would be effective in treating the metastases. Moreover, post-mortem analysis of tumor metastasis samples immediately frozen or fixed for comparison to similarly fixed matching primary tumor samples comes too late for the patient.
Previously, there existed no method to accurately and systematically compare the expression of tumor gene determinants in both primary tumor and metastases available in pathological archives. Most patient derived pathological samples are routinely fixed and paraffin-embedded (FPE) to allow for histological analysis and subsequent archival storage. Thus, most biopsy tissue samples are not useful for analysis of gene expression because such studies require a high integrity of RNA so that an accurate measure of gene expression can be made. Currently, gene expression levels can be only qualitatively monitored in such fixed and embedded samples by using immunohistochemical staining to monitor protein expression levels.
The use of frozen tissue by health care professionals as described in Leichman et al., and Reed et al., poses substantial inconveniences. Rapid biopsy delivery to avoid tissue and subsequent mRNA degradation is the primary concern when planning any RNA-based quantitative genetic marker assay. The health care professional performing the biopsy, must hastily deliver the tissue sample to a facility equipped to perform an RNA extraction protocol immediately upon tissue sample receipt. If no such facility is available, the clinician must promptly freeze the sample in order to prevent mRNA degradation. In order for the diagnostic facility to perform a useful RNA extraction protocol prior to tissue and RNA degradation, the tissue sample must remain frozen until it reaches the diagnostic facility, however far away that may be. Maintaining frozen tissue integrity during transport using specialized couriers equipped with liquid nitrogen and dry ice, comes only at a great expense.
Moreover, routine biopsies generally comprise a heterogenous mix of stromal and tumorous tissue. Unlike with fresh or frozen tissue, FPE biopsy tissue samples are readily microdissected and separated into stromal and tumor tissue and therefore, offer an advantage over the use of fresh or frozen tissue. However, isolation of RNA from fixed tissue, and especially fixed and paraffin embedded tissue, results in highly degraded RNA, which is generally not thought to be applicable to gene expression studies.
We report here a significant association between levels of tumor determinant gene expression in primary tumor with expression of the same tumor determinant gene in matching metastases in archival samples. Accordingly, it is the object of the invention to provide a method of quantifying mRNA from primary tumor tissue in order to provide an early prognosis for genetically targeted chemotherapies to treat tumors throughout the patient's body.